1. Field of the Invention
The present invention relates to a manufacturing method for a silicon wafer to be used as a substrate of semiconductor devices.
2. Description of Related Art
With trends toward high integration of semiconductor devices in recent years, requirement for quality of a silicon wafer to be used as a substrate of such semiconductor devices is becoming severer. In particular, there is an eager demand for the development of a silicon wafer having less grown-in defects in the device active region.
A technique of performing heat treatment on a silicon wafer is well known as a process for reducing such grown-in defects.
As one example of such a technique, there is a technique of heat treating a silicon wafer at a temperature of 1000° C. or higher and 1350° C. or lower for 50 hours or less in a hydrogen and/or inert gas atmosphere, followed by oxidation heat treatment at a temperature range of 800° C. or higher and 1350° C. or lower for 50 hours or less (for example, Japanese Patent Unexamined Publication JP-A-11-260677).
There is also known a technique of heat treating a silicon single crystal wafer at a temperature of from 1100 to 1300° C. in a non-oxidizing atmosphere for 1 minute or more and heat treating the resulting wafer continuously at a temperature of from 700 to 1300° C. in an oxidizing atmosphere for 1 minute or more without cooling it to a temperature less than 700° C., thereby forming a silicon oxide film on the surface of the wafer (for example, Japanese Patent Unexamined Publication JP-A-2001-144275).
In recent years, a technique for subjecting a silicon wafer to rapid heating/cooling thermal process (RTP: Rapid Thermal Process) is known as a technique of producing, in a high productivity and an easy manner, a silicon wafer with few defects in the surface layer of the wafer.
As one example, there is known a technique of heating a material for substrate obtained from a silicon single crystal having an oxygen concentration of from 11 to 17×1017 atoms/cm3 (ASTM F-121, 1979) at from 1100 to 1280° C. for from 0 to 600 seconds in an atmosphere containing nitrogen in an amount of 90% or more and then cooling it at a cooling rate of from 100 to 25° C./sec in an atmosphere switched to that containing oxygen in an amount of 10% or more (for example, Japanese Patent Unexamined Publication JP-A-2003-115491).
The heat treatment technique described in the JP-A-11-260677 is however not preferred because it has poor productivity because long heat treatment time is necessary and in addition, slip tends to occur during heat treatment.
The heat treatment technique described in the JP-A-2001-144275 is also not preferred because it has also poor productivity due to a substantially long heat treatment time and in addition, slip tends to occur during heat treatment.
In the heat treatment technique described in the JP-A-2003-115491, a nitride film is inevitably formed on the surface of the silicon wafer as a result of heat treatment in an atmosphere containing nitrogen in an amount of 90% or more. Thus, a step for removing the nitride film, such as etching process, is required so that the number of manufacturing steps is increased. Therefore, this technique is also not preferred.